“Adults are developing food allergies as adults to foods they could previously tolerate. Peanut allergy is still the most frequent allergy in kids and has increased slightly,” Dr. Ruchi Gupta, lead author of the study told Global News.

“Food allergies are often seen as a condition that begins in childhood, so the idea that 45 per cent of adults with food allergies develop them in adulthood is surprising,” she said in a statement.

“Usually with shellfish allergies in adults, it is almost always intertwined with dust mites and cockroaches,” he tells Global News. He adds allergens found in dust mites, for example, are similar to those found in crustaceans, so when rates of one goes up, so does the other.

This is also similar for people with tree nut allergies, he adds. They may also react to birch tree pollen. “The categories of nut and shellfish is linked to other allergies first.”

Gupta adds there are no real explanations as to why these rates continue to rise. “Many speculate due to changes in our societal behaviours,” she says. “The hygiene hypothesis, changes in how and what we eat, [and] changes in our microbiome.”

The research found black, Asian and Hispanic adults in the U.S. had a greater risk of developing food allergies, especially shellfish and peanut ones. Allergy researcher Dr. Christopher Warren added Asian adults were 2.1 times more likely to report shellfish allergies compared to white adults.

“Hispanic adults reported a peanut allergy at 2.3 times the frequency of white adults. Because many adults believe food allergies mostly affect children, they may not think to get tested. It is important to see an allergist for testing and diagnosis if you are having a reaction to a food and suspect a food allergy,” he said in a statement.

WATCH: How you can help those with food allergies

Researchers note peanut allergies in children, in particular in the U.S., have increased by 21 per cent since 2010.

“The good news is that parents now have a way to potentially prevent peanut allergy by introducing peanut products to infants early after assessing risk with their pediatrician and allergist.” Gupta continued.

The most common adult-onset allergies

Looking at more than 53,000 U.S. households between October 2015 and September 2016 to determine rates among children, Gupta and her team found tree nuts, for example, increased from 18 per cent from 2010, while shellfish allergies increased by seven per cent.

The network notes one in 13 Canadians (or 2.5 million people) were affected by at least one type of food allergy.

Testing for food allergies

Fischer adds there is still confusion between allergies and intolerance, and some people may not know the difference between the two. Allergies are allergic reactions to proteins, he adds, and this can include symptoms of vomiting, hives or shortness of breath.

Food intolerance is often with lactose or gluten, and can result in digestion issues or stomach distress. “[People] assume they have an allergy and they avoid a lot of food,” he says.

The best way to figure out exactly what you have is by getting an allergy test. Not only will you have a diagnosis, but Fischer adds an allergy specialist will be able to make further assessments, especially if allergies run in your family.

And for researchers like Gupta, she says a lot more work has to be done to make sure the rates drop in the next 25 years.

“We have new potential treatment currently in trials. Research is better at understanding possible predictors to food allergies and moving fast, so I am hopeful we will start to see a decrease in the future.”